The present invention relates generally to fabric reinforced elastomeric diaphragms employed for piston operation in railway type air brake valve devices and, in particular, to thin section elastomeric diaphragms.
In such railway type air brake valve devices, as ABD, ABDW, and ABDX control valves, diaphragm mounted pistons are subject to operation with pneumatic pressures as high as 110 psi. Accordingly, particular emphasis has been placed on designing a clamping arrangement for such diaphragms that will hold the diaphragm against pull-out forces, and at the same time maintain a pressure seal at the diaphragm clamping point.
While such diaphragm clamping arrangements have proven successful over time, the service life of the diaphragm itself has been limited by the tendency of the diaphragm to develop cracks and eventually fail. Such cracking has been found to occur in the convolution area of the diaphragm and particularly on conical type diaphragms that are molded without a convolution. Whereas these diaphragms form a convolution during assembly, such convolution being necessitated by the long travel requirement of the aforementioned control valve pistons, in order for the convolution to form, the outside surface tends to become stretched and the inside surface tends to be compressed. This causes the diaphragm to "bunch up" and thereby produce wrinkles along the inside hoop area of the convolution. It is along the lines of these wrinkles that the diaphragm is predisposed to cracking and eventual failure. It will be appreciated that the thicker the diaphragm for a given radius of curvature of the convolution, the greater the "bunching" tendency and consequently the resultant development of cracks.